Small diameter radiation sensor cable

ABSTRACT

A duplex plastic optical fiber may be used to create a dual detector system, which allows for the detection of two distinct areas of radiation in a single sensor cable device. A fiber cap holds a scintillating fiber and slides over an exposed portion of an optical fiber adjacent to an end of the optical fiber to create a concentric connection for a radiation sensor cable used in medical radiation therapy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to 61/481,503, filed May 2, 2011, andincorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

N/A

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

N/A

FIELD OF THE INVENTION

This invention relates to radiation sensor cables of very smalldiameter, such that they are suitable for use in medical applications.

BACKGROUND OF THE INVENTION

A scintillator is a special material that exhibits scintillation—theproperty of luminescence when excited by ionizing radiation. Luminescentmaterials, when struck by an incoming particle, absorb its energy andscintillate, in other words they reemit the absorbed energy in the formof light.

A scintillation detector or scintillation counter is obtained when ascintillator is coupled to a light sensor such as a photomultiplier tube(PMT), photodiode, PIN diode or CCD-based photodetector. The lightsensor will absorb the light emitted by the scintillator and reemit itin the form of electrons via the photoelectric effect. The subsequentmultiplication of those electrons (sometimes called photo-electrons)results in an electrical pulse that can be analyzed and providesmeaningful information about the particle that originally struck thescintillator. In this way, the original amount of absorbed energy can bedetected or counted.

The term “plastic scintillator” typically refers to a scintillatingmaterial where the primary fluorescent emitter, called a fluor, issuspended in a solid polymer matrix. While this combination is typicallyaccomplished through the dissolution of the fluor prior to bulkpolymerization, the fluor is sometimes associated with the polymerdirectly, either covalently or through coordination, as is the case withmany Li₆ plastic scintillators. Polyethylene naphthalate has been foundto scintillate without any additives and is expected to replace existingplastic scintillators due to its higher performance and lower price.

The advantages of plastic scintillators include fairly high light outputand a relatively quick signal, with a decay time between 2-4nanoseconds. The biggest advantage of plastic scintillators, though, istheir ability to be shaped, through the use of molds or other means,into almost any desired form with a high degree of durability.

In the field of medical radiation therapy, plastic scintillationdetectors are used to convert radiation energy into light energy, andthe light photons are counted to accurately determine the radiationdose. The scintillating plastic must transfer its photons to a devicethat can read them, which is commonly done by coupling one or morescintillating fibers to one or more plastic optical fibers (POF). ThePOF is then connected to a device that can read and analyze the opticaloutput.

Manufacturing a high volume of such sensor cables is difficult becausean accurate and repeatable connection of the plastic scintillator fiberto the plastic optical fiber is required. The problem arises fromworking with small diameter optical fibers that must be constructedaccurately, yet at a low cost.

The current process used to create a sensor cable with a plasticscintillation detector relies on many precise, time-consuming steps.First, both ends of the scintillating fiber must be cut and polished.These cuts and polishes are difficult to do because the diameter (1 mm)and length (2 mm) of the scintillation fiber are very small. Next, theoptical fiber must be cut, stripped and polished. Then the scintillatingfiber is attached to the optical fiber with optical adhesive. A smallpiece of the optical fiber's jacket can be used to hold the two fibersin place when adhering. This step is challenging due to the small sizeof the fibers and the need to perfectly align their cores. A black paintor coating is then applied to the distal end of the fiber in order tokeep the assembly light tight. The finished assembly is vulnerable tobreakage because reliance is placed on the strength of the epoxy bond tohold the assembly together, and on a soft jacket material (PE or PVC) tohold the assembly in alignment. Due to the labor intensive process andtime consuming steps, it is very expensive to produce a detector in thisfashion, and the process also introduces variability from detector todetector. The current process also uses twist on (FC) or screw on (SMA)metal-bodied fiber connectors at the other end of the sensor cable.Applying these connectors adds more time to the process, and the FC andSMA connectors are expensive.

Therefore, a need exists for a novel manufacturing process and systemfor a radiation sensor cable to solve these problems.

BRIEF SUMMARY OF THE INVENTION

Generally speaking, the invention relates to tiny plastic scintillatordetector cables, suitable for medical uses, methods of fabricating sameand various applications therefor. The tiny and inexpensive scintillatordetectors are used to assess radiation dosage in real time, and providea tremendous advance in the field, which heretofore has lacked suchtiny, inexpensive detectors for use inside a body cavity at the actuallocation of the radiation therapy. Applications include stereotacticradiosurgery/stereotactic radiotherapy (SRS/SRT), intensity modulatedradiation therapy (IMRT), dynamical arc therapy, tomotherapy treatments,and any similar application where radiation sensing in a small area isneeded, including non-medical applications.

In one embodiment, the plastic scintillator detector cable consists of asingle, short length of scintillator fiber operably coupled to asuitable length of optic fiber, which has a standard data coupler orconnector at the end of the cable opposite the scintillator fiber. Thescintillator detector is thus at the distal end of the cable and asuitable data coupler is at the proximal end, and the entirety of thecable is enclosed in a flexible, opaque covering.

In another embodiment, the cable is hardwired directly to aphotodetector, thus avoiding connector use. However, the use of theconnector may be preferred as it allows for quick and easy replacementof damaged cables.

In another embodiment, the cable has at least two separate, but closelyjuxtaposed, plastic scintillator detectors. The two detectors areparallel, but offset from one another in the longitudinal axis, so thatradiation can be simultaneous assessed at two ends of a target, such ason either end of the prostrate or both ends of an irradiated throatarea, and the like.

In another embodiment, an additional fiber optic cable without plasticscintillator detector can be added thereto, and can serve the functionof allowing the subtraction of any background signal, which can arisefrom the inherent dark current of the PMT or mostly Cerenkov lightgenerated in the fibers. However, these effects are negligible forphoton beams, and thus this extra cable is not needed.

Additional plastic scintillation detectors can be added if desired toassess radiation in three or more places along a longitudinal radiationaxis. However, single scintillation detectors can also be used wheresufficient for the application in question, e.g., where the area to beirradiated is quite small.

Where it is desired to assess radiation levels over more than one axis,e.g., with a larger radiation zone, a second plastic scintillatordetector cable can be added, somewhat offset from the first cable(offset in the axis perpendicular to the cable), although this willobviously increase the overall size and cost of the device accordingly.

The scintillator detector can be combined with any medical devicesuitable for insertion into a body cavity, such as a prostate balloon,vaginal balloon, catheter, needle, brachytherapy-applicator, surgicalimplements, and the like.

For balloon usage, a small strip of balloon material can be welded tothe outer surface thereof, and the scintillator cable threadedtherethrough, thus reliably positioning the detector on the outersurface of the balloon. Alternatively, the cable can be placed insidethe balloon and held with one or more spot welds and/or small strips ofballoon material or other attachment means.

For solid medical devices, such as brachytherapy applicators, a smalltube can be affixed thereto, and the tiny cable threaded inside thesmall tube, or the cable can be affixed directly to the applicator.Alternatively, a removable balloon can be provided for the applicator,such as is already described. The cable can also be threaded inside acatheter or needle, and other device used to access a body cavity.

The scintillator detector cable has any suitable data connector oradaptor at the proximal end thereof, and is plugged into any existing ordedicated signal detection and computer system for collecting, analyzingand outputting the data collected by the scintillator detector.

Suitable connectors include FDDI, ESCON, SMI, SCRJ, and the like, andwill of course vary according to the system that is intended to be usedwith the scintillator detector cable. The data connectors can be singleconnectors, even for a dual or triple detector embodiment, butpreferably a dual connector is used for the dual detector embodiment,etc., which keeps the cables neat and can prevent plugging sensors intothe wrong channels if the connector has asymmetry.

Because the scintillator detector is quite small, novel fabricationmethods were developed to allow cost effective, reliable manufacture andassembly therefore. A special cap was therefore designed to allow thescintillator fiber to be reliably connected to the fiber optic cable.This cap is essentially tube shaped with a blind end, such that thescintillator fiber fits entirely into the blind end, and the fiber opticcable fits behind it. Thus, the hollow interior closely holds the endsof the two fibers in close juxtaposition (direct contact or “abutting”)without the need for any adhesive on the ends of the two fibers, whichgreatly improves both sensitivity and reliability. The hollow interioris thus shaped to closely fit the naked fibers, and in many instanceswill have a circularly cross-section, although this can of course varyif the fiber cross section is varied.

The tube could also have two open ends, but one closed end is preferredas better protecting the fragile fiber, and avoiding a closure step.However, a dual opening cap may be preferred for longer fibers since thedual opening variant can be loaded from either end. The cap can alsocomprise two components fitted together, e.g., by threadable or snapfits ends, but the unitary construction is the simplest to make and use.Where the tube has an open end, it can be covered with heat shrinkabletubing, a jacket, opaque coating, snap fit lid, or any other means ofmaking it light tight, and preferably water tight. A snap fitting lidcan easily be attached to the tube with a small hinge, thus providing aunitary construction that can be made by injection molding, and stillallowing tube loading from both ends.

The cap can also be designed with a small extra space left inside forplacement of a fiducial marker. In this way, an imaging device, such asa tungsten, gold, barium, carbon or any other radiopaque or reflectivepellet can be placed in the tip of the cable and assist in its placementinside the body. Alternatively, the pellet can be placed outside thecap, e.g., on the outer surface or tip thereof. In fact, the cap can beinjection-molded with a small snap fit recess into which an imagingpellet can be snap fit.

The blind cap can be affixed to the optical fiber using an optional beadof adhesive at the open end, which will thus only touch the side of thenaked optical fiber, or an external clamp can be used, or the blind capitself can be made of heat shrinkable material for a tight fit. However,we have found that a harder plastic functions best to keep the twocables aligned, and prefer a high impact polystyrene or similar resinfor this purpose. Preferable resins have a hardness of 45 or below, andpreferably has 30-40 Shore D.

Alternatively or in addition thereto, an exterior coating of heatshrinkable material can be added thereto for good strength and fit. Theshrink tubing covers at least the detector end of the device andprotects the detector, while keeping the components together in a tightbundle that remains flexible and can move in all directions. Where thecap is opaque, part of the cap can protrude from the heat shrinkabletubing. The shrink tubing can also cover most or all of the cable, butthis will generally not be needed since plastic optical fibers areusually already jacketed, although the heat shrinkable tubing will alsofunction to keep the fibers tightly bundled and thus may be of benefit.

Suitable plastics for the blind cap include high impact polystyrene,polybutadiene, acrylonitrile butadiene styrene, polyvinyl chloride,polycarbonate, polyacrylate, polyethylene terephthalate glycol, highdensity polyethylene, polypropylene, high impact rigid polyvinylchloride, and polytetrafluoroethylene, and blends and copolymersthereof. Preferred materials are opaque in color to keep the assemblylight tight. Alternatively, the cap can be covered in an opaque materialand thus plastics with high clarity can be used, such as polycarbonateand polyacrylate.

Also preferred, the blind cap is constructed from a water equivalentplastic so as to not perturb the radiation dosage, and it is known inthe art how to assess water equivalence at different energy ranges.Where the plastic is not quite water equivalent, it is known how toapply a scaling factor. See D. Mihailescu and C. Borcia, WaterEquivalency Of Some Plastic Materials Used In Electron Dosimetry: AMonte Carlo Investigation, Romanian Reports in Physics, Vol. 58, No. 4,P. 415-425, 2006 (incorporated by reference herein).

A hot knife blade is preferably used for cutting each fiber, therebyeliminating the need for polishing. A soldering iron set to 700° F. maybe used with a fine point carbon steel blade having a thickness of0.0235 inches (0.06 cm). Other hot knifes, temperatures, and bladethicknesses are also contemplated, and it is known how to vary thetemperature with the material being used. Many industrial hot-knives areavailable for use, and cutting blocks that function to ensure a 90° cutare also commercially available. Although a hot knife may be preferred,other cutting methods can be used, including laser, water jet, diamondsaw, and the like.

Many suitable jacket plastics are known, and preferably are opaqueplastics of low antigenicity or medical grade, although any plastic canbe used and combined with an appropriate biocompatible coating. Suchmaterials include low smoke zero halogen (LSFH), polyvinyl chloride(PVC), polyethylene (PE), polyurethane (PUR), polybutylene terephthalate(PBT), polyamide (PA), and the like.

Particularly preferred jacket materials are medical grade polyurethanesdue to their lack of plasticizers and which are available in a varietyof hardness, ranging from 60 Shore D to 90 Shore A. Particularlypreferred are softer plastics of 70-80 Shore A and which give the cableconsiderably flexibility combined with sufficient strength. However, thepolyurethane may need to overlay an opaque plastic, such as black PVC,unless opaque pigments are added thereto or an opaque paint is appliedthereto.

Also preferred are cable materials that withstand sterilizationprocedures, such as autoclaving, gamma irradiation or chemicaltreatments, although sterilization may be optional if combined with aseparately sterilizable balloon that can completely contain the sensor,or if a non-sterile device is needed, e.g., for rectal applications.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims or the specification means one or more thanone, unless the context dictates otherwise.

The term “about” means the stated value plus or minus the usual marginof error of measurement, or plus or minus 10% if no method ofmeasurement is indicated.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or if thealternatives are mutually exclusive.

The terms “comprise,” “have,” and “include” (and their variants) areopen-ended linking verbs and allow the addition of other elements whenused in a claim.

The phrase “consisting of” is a closed linking verb and does not allowthe addition of any other elements.

The phrase “consisting essentially of” occupies a middle ground,allowing the addition of non-material elements such as labels,instructions for use, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained with thefollowing detailed descriptions of the various disclosed embodiments inthe drawings, which are given by way of illustration only, and thus arenot limiting the invention, and wherein:

FIG. 1A is a perspective view of a partially coiled duplex scintillatorcable, with adaptor at the proximal end and exploded scintillatordetectors at the distal end.

FIG. 1B is a detail exploded view in area B of FIG. 1A of two exposedduplex optical fibers, two scintillating fibers, two rings of adhesive,two fiber caps, and a heat shrink tubing.

FIG. 1C is a detail view in area C of FIG. 1A showing the adaptor.

FIG. 2A is a plan view of the distal end of the duplex plastic opticalfiber of FIG. 1.

FIG. 2B is a cross section of the view in FIG. 2A through lines 2B-2B.

FIG. 3A is an perspective view of the fiber cap of the invention.

FIG. 3B is a plan view of FIG. 3A.

FIG. 3C is a cross-sectional view along line 3C-3C of FIG. 3B.

FIG. 4 is a flow diagram of the assembly process.

FIG. 5 is a perspective an open cap with hinged snap fitting lid.

DETAILED DESCRIPTION OF THE INVENTION

The parts of FIG. 1A-C are listed herein and preferred materialsprovided:

Part No. Description Preferred materials 1 Optical fiber MITSUBISHISUPER ESKA 1 MM DUPLEX PLASTIC OPTICAL FIBER SH4002 2 Scintillatingfiber BCF-60 SAINT GOBAIN SCINTILLATING FIBER PEAK EMMISSION 530 NM 3fiber cap HIGH IMPACT POLYSTYRENE 4 Adhesive EPOXY TECHNOLOGIES EPO- TEK301 5 Heat shrinkable RAYCHEM THERMOFIT CGPE-105 tubing HEAT-SHRINKABLETUBING 6 Lot Code Label NA 8 Adaptor SCRJ CONNECTOR 11 Coiled section ofcable. NA Protruding ends allows for calibration of each cable and is apreferred packaging method.

Turning to FIG. 1, the duplex scintillation detector cable 10 has afirst and second optical fibers 1. The jacket or covering 1A has beenstripped or removed from the portion of the first optical fiber 1adjacent to the distal ends of each fiber (see also FIG. 2B), leaving aportion of each optical fiber 1B exposed. First and second scintillatingfibers 2 are shown, along with drop of adhesive 4 and fiber cap 3. Thelength of scintillating fibers 2 can be varied, according to neededsensitivity and size of area to be assessed, but typically 1-10 mm oflength will suffice. We have used 2-3 mm lengths in prototypes.

The scintillating fibers 2 fit into the fiber caps 3, followed by thenaked optic fibers 1B, and a drop of epoxy 4. Heat shrink tubing 5covers the components, which are shown assembled in FIGS. 2A and 2B. Atthe far end, an adaptor 8 is found, in this case a dual jack adaptor.Label 6 is also shown, but may be placed anywhere on the cable or evenon packaging and is not considered material. There is no adhesive 4 onthe abutted ends or faces of the respective scintillating fibers 2 andoptical fibers 1B, thus signal is optimized.

The duplex optical fiber 1 may be a Super Eska 1 mm duplex plasticoptical fiber SH4002 available from Mitsubishi Rayon Co., Ltd. of Tokyo,Japan, although other duplex optical fibers are also contemplated.Although duplex optical fibers 1 are shown, it is also contemplated thata single optical fiber may be used or additional fibers can be added.

The scintillating fibers 2 may be a BCF-60 scintillating fiber peakemission 530 NM available from SAINT-GOBAIN CERAMICS & PLASTICS™, Inc.of Hiram, Ohio, although other scintillating fibers are alsocontemplated.

FIG. 2A shows a plan view of the detector end of cable and line 2B-2B,through the center of the cable. FIG. 2B is a cross-section at line2B-2B. Seen here are scintillator fibers 2, inside cap 3, andimmediately distal to naked optical fibers 1B. Heat shrink tubing 5covers the detector/distal end of the cable, thus making a detectorassembly. Tubing 5 is shown with a small amount of the distal-most capprotruding, but placement can vary as long as the bundle is tightly heldand opaque. Optical fibers past the cap 3 are covered by jacket 1A. Abead of optional adhesive 4 is placed at the end of cap 3 and does nottouch the ends of the fibers, but a small amount can travel by capillaryaction between optical fiber 1B and the inside of cap 3.

The fiber cap 3 is shown in more detail in FIG. 3A-C. Cap 3 has an openend 31, a closed end 33 defining a hollow interior 35 into which fibers1, 2 tightly fit. The cap 3 is constructed from a water equivalentmaterial, such as polystyrene, and may be opaque in color to keep theassembly light tight. A high impact polystyrene may be used, with aMold-Tech 11010 texture or smoother, although other materials andtextures are also contemplated.

The use of a pair of plastic optical fibers 1 and pair of scintillatorfibers 2 allows a dual detector system using two fibers jacketedtogether to form a single cable. However, the detectors are stillindependent and give separate measurements of radiation dosage at eachlocation. The duplex scintillator cable 10 combined with thelongitudinally offset positioning of two scintillating fiber tips 2allows for the detection of two distinct areas of radiation in a singlesensor cable device. Additional scintillating fibers and optical cablesmay be added to the cable for additional detection areas.

The small length of shrink tubing 5 covers the detector end of thedevice and protects the detectors 2 while keeping the assembly togetherin a tight bundle. The bundle is allowed to flex and move in alldirections. If desired, the shrink tubing can cover a longer length ofthe cable than is shown herein.

The diameter of the cable herein described is very small, and the deviceis thus tiny enough to be added to existing medical devices for avariety of radiation applications. Preferably, the cable diameter(excluding the proximal adaptor of course) is less than 5 mm, andpreferably less than 4, 3, or 2 mm. Yet, in spite of its small size, thedevice is robust and easily manufactured.

A hot knife may be used to make the process more efficient. By cuttingeach optical fiber distal end 1 and each scintillating fiber 2 with thehot knife blade, the polishing step of the past may be eliminated. Thehot knife cuts a smooth and uniform fiber surface with no scraping orcracking, producing light transmittance results on par with polishedfibers.

The optical adhesive used in the past may also be omitted from themethod and system. Instead of using adhesive between the exposed opticalfiber ends, as is done in the prior art, the optical and scintillatingfibers are aligned using the fiber cap 3 and secured by applyingoptional adhesive 4 only to the open end 31 of the cap 3. The bond isbetween the cap 3 and the exposed sides of the optical fiber 1 andincreases the strength of the assembly and reduces the accuracy neededat the adhesive joint, however the adhesive is optional, as is theshrink tubing.

One embodiment of the assembly process is illustrated in FIG. 4, and isas follows.

Step 1: Cut the plastic optical fiber 1 to length using the hot knife atstep 100.

Step 2: Cut the plastic scintillation fiber 2 to length using the hotknife system at step 105.

Step 3: Strip back the jackets (if any) on each fiber 1, 2 to aspecified length at step 110.

Step 4: Insert the bare scintillation fiber 2 into the scintillating cap3 at step 115 and gently push until seated at the blind terminus.

Step 5: Insert bare optic fiber 1 into scintillating cap 3. Gently pushuntil the optical fiber 1 is in good contact with the scintillationfiber 2 at step 120.

Step 6: Apply the optional bead of the UV cure epoxy or other adhesive 4around the open end 31 of the fiber cap 3 where the optical fiber 1 isexposed. No epoxy 4 contacts the scintillation fiber 2 or the respectiveabutting ends of the two fibers because only a small amount of adhesiveis used.

Step 7: Slide the optional heat shrink tubing 5 over the distal end ofthe sensor cable 10 so that the edge of the heat shrink 5 isapproximately 1 mm away from the distal end of the most distalscintillation cap 3, although it can also completely contain same ormore can protrude, as desired. Use a heat gun or oven to shrink down thetubing 5 over the detectors 2 at step 130.

Step 8: Attach an appropriate connector 8 to the proximal end of thecable 10 opposite the detectors 2 at step 135.

The cable is thus fabricated, and can be labeled, packaged andsterilized, as needed.

The process allows for a much quicker and more accurate assembly than inthe past. The cable assembly may be produced in high volumes withexcellent repeatability. Variations on the methods are contemplated, andfewer steps are also contemplated.

FIG. 5 shows an open ended cap 40 that can be of unitary constructionmade by injection molding. The tube 47 has two open ends 48, 49, each ofwhich can accessed for manufacture of the cable. Once the two fibers arein place, lid 43, held with flexible thin hinge 41, snaps shut, annularedge or lip 45 serving a snap fit function and making the cap light andwater tight.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof. Various changes in the details ofthe illustrated construction can be made within the scope of the presentclaims without departing from the true spirit of the invention. Thepresent invention should only be limited by the following claims andtheir legal equivalents.

1. A radiation sensor cable, comprising: a. a first distal fiber caphaving a tubular shape, hollow interior and a closed end and an openend, b. a first plastic optical fiber having a distal end and a proximalend; c. a first plastic scintillation fiber; wherein said plasticscintillation fiber fits completely inside said fiber cap at said closedend and is directly abutted to said distal end of said plastic opticalfiber which partially fits inside said fiber cap and partially protrudestherefrom; d. an opaque jacket enclosing said plastic optical fiber andoptionally said fiber cap; and a proximal data adaptor operablyconnected to said proximal end of said plastic optical fiber.
 2. Theradiation sensor cable of claim 1, further comprising second parts a, b,and c, contained inside said opaque jacket and operably connected toeither a dual data adaptor or two data adaptors, and wherein said firstand said second fiber caps are longitudinally offset from each other. 3.The radiation sensor cable of claim 1, further comprising a heatshrinkable tubing covering at least a portion of said first fiber capand said first plastic optical fiber.
 4. The radiation sensor cable ofclaim 1, having a maximum cable diameter (excluding said data adaptor)of less than 5 mm.
 5. The radiation sensor cable of claim 4, having amaximum cable diameter of less than 3 mm.
 6. The radiation sensor cableof claim 4, having a maximum cable diameter of less than 2 mm.
 7. Theradiation sensor cable of claim 4, having a maximum cable diameter ofabout 1 mm.
 8. A radiation sensor cable, comprising: a. first and secondfiber caps, each having a tubular shape, hollow interior and a closedend and an open end, and being made from a hard polymer of durometerless than 45 Shore D, b. first and second plastic optical fibers, eachhaving a distal end and a proximal end; c. first and second plasticscintillation fibers; wherein said first plastic scintillation fiberfits completely inside said first fiber cap at said closed end and isdirectly abutted to said distal end of said first plastic optical fiberwhich partially fits inside said first fiber cap and partially protrudestherefrom; wherein said second plastic scintillation fiber fitscompletely inside said second fiber cap at said closed end and isdirectly abutted to said distal end of said second plastic optical fiberwhich partially fits inside said first fiber cap and partially protrudestherefrom; wherein said first and second fiber caps are longitudinallyoffset from each other, d. an opaque jacket enclosing at least a portionof said first and second fiber caps and first and second plastic opticalfibers; and e. a proximal dual data adaptor operably connected to saidproximal ends of said first and second plastic optical fibers; whereinthe maximum diameter of said radiation sensor cable is less than 2 mm(excluding said proximal dual data adaptor).
 9. The radiation sensorcable of claim 8, wherein the proximal dual data adaptor is an SCRJadaptor.
 10. A method of manufacturing a radiation sensor cable formedical radiation therapy, comprising the steps of: a. cutting ascintillation fiber to a predetermined scintillation fiber length; b.inserting said scintillation fiber in a fiber cap having a length and aninterior hollow and an open end and a closed end, wherein thepredetermined scintillation fiber length is less than said length ofsaid fiber cap; c. inserting a first end of an optical fiber into saidcap behind said scintillation fiber; d. pushing said optical fiber untilit contacts said scintillation fiber to make a first detector assembly;and e. adding a data adaptor to a second end of said optical fiber toform a radiation sensor cable.
 11. The method of claim 10, furthercomprising adding a drop of adhesive to said open end of said cap. 12.The method of claim 10, wherein said scintillation fiber and saidoptical fiber are each cut with a hot knife prior to insertion into saidcap.
 13. The method of claim 10, further comprising inserting said firstdetector assembly into heat shrinkable tubing and heat shrinking to fit.14. The method of claim 10, further comprising the steps of adding asecond detector assembly made according to steps a-e to said radiationsensor cable.
 15. The method of claim 10, further comprising the stepsof adding a second detector assembly made according to steps a-e to saidradiation sensor cable, but proximal to said first detector assembly,and inserting said first and second detector assemblies inside heatshrinkable tubing and shrinking to fit.
 16. The method of claim 10,wherein said fiber cap is made from a hard polymer of durometer lessthan 45 Shore D.
 17. A fiber cap for holding a plastic optical fiberabutted to a plastic scintillation fiber; said fiber cap comprising atubular shape and an interior hollow and an open end and a closed end,wherein fiber cap is made only of a hard opaque plastic of durometer30-40 Shore D by injection molding, and said interior hollow is sized toclosely fit a plastic scintillation fiber abutted against a plasticoptical fiber.
 18. A fiber cap, said fiber cap consisting of a tubularshape and an interior hollow and an open end and a closed end, whereinsaid fiber cap is made of a hard opaque plastic of durometer 30-40 ShoreD by injection molding, wherein said fiber cap contains a length ofplastic scintillation fiber in said hollow interior at said closed end,and a length of plastic optical fiber directly abutting said length ofplastic scintillation fiber and protruding from said open end of saidfiber cap.
 19. A radiation sensor cable, comprising: a. first and secondfiber caps, each having a tubular shape and hollow and being made from ahard polymer of durometer less than 45 Shore D, b. first and secondplastic optical fibers, each having a distal end and a proximal end; c.first and second plastic scintillation fibers; wherein said firstplastic scintillation fiber fits completely inside said first fiber capand is directly abutted to said distal end of said first plastic opticalfiber which partially fits inside said first fiber cap and partiallyprotrudes therefrom; wherein said second plastic scintillation fiberfits completely inside said second fiber cap and is directly abutted tosaid distal end of said second plastic optical fiber which partiallyfits inside said first fiber cap and partially protrudes therefrom; saidfirst and second fiber caps are longitudinally offset from each other,d. an opaque jacket enclosing at least a portion of said first andsecond fiber caps and first and second plastic optical fibers.